This invention relates to a method for treating the reactive silicon powder obtained as a reaction residue of the reaction of metallic silicon and a chlorinated hydrocarbon to prepare organochlorosilanes or the reaction of metallic silicon and hydrogen chloride to prepare chlorosilanes. The instant invention is an improvement to the invention of another U.S. patent application which is filed concurrently with the instant application. The application in reference, which was filed on behalf of Hidehiko Hosokawa and which is also entitled METHOD FOR TREATING ACTIVATED SILICON POWDER, was filed on evendate herewith.
The reaction of metallic silicon and a chlorinated hydrocarbon to prepare organochlorosilanes and the reaction of metallic silicon and hydrogen chloride to prepare chlorosilanes is widely practiced on a commercial-scale. The reaction of metallic silicon with a chlorinated hydrocarbon can be such reactions as (1) the preparation of methylchlorosilanes such as methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, or methyldichlorosilane from the reaction of metallic silicon and methyl chloride; (2) the preparation of phenylchlorosilanes such as phenyltrichlorosilane, diphenyldichlorosilane, or phenyldichlorosilane from the reaction of metallic silicon and chlorobenzene; (3) the preparation of ethylchlorosilanes from metallic silicon and ethyl chloride. The reaction of metallic silicon and hydrogen chloride produces chlorosilanes such as tetrachlorosilane and trichlorosilane.
Various methods are practiced in carrying out the reactions, supra. Generally, the metallic silicon is finely divided and is reacted with the chlorinated hydrocarbon or hydrogen chloride in a fluidized bed. A catalyst such as copper is generally added to the reaction. However, regardless of the specific method of carrying out the reactions, supra, and distillation of the produced organochlorosilanes or chlorosilanes not all of the metallic silicon will react and a portion of the starting metallic silicon will finally remain as a residue from the reaction. The portion of the starting metallic silicon that will remain as a residue will depend upon the particular starting materials, the purpose of the run, and the operating conditions.
The metallic silicon residue poses a safety hazard, since it is still chemically reactive. This powdered reaction residue readily undergoes spontaneous combustion upon contact with the atmosphere and reacts with water to produce hydrogen. The particle size of this powdered, reactive silicon reaction residue will vary, but generally the particle size is in the range of 1 to 200 microns. The silicon powder, being a powder, is difficult to handle for purposes of moving to waste disposal or to means of reuse. Before the instant invention, no method has been disclosed for treating the reactive silicon powder to reduce the powder's reactivity and to improve its handling.
The objective of the instant invention is to provide ease of handling and to reduce the reactivity of the silicon powder, obtained as a reaction residue from the preparation of organochlorosilanes or chlorosilanes from metallic silicon and a chlorinated hydrocarbon or hydrogen chloride, to a practical level of safe operation.
The instant invention achieves this objective, supra, by the method of combining the reactive silicon powder reaction residue, obtained from the preparation of organochlorosilanes or chlorosilanes from the reaction of metallic silicon with chlorinated hydrocarbons or hydrogen chloride, with water; granulating the silicon powder; and then coating the granules with an inert inorganic powder.